This invention relates to a heating method, and in particular to a heating method wherein a light transmissive columnar body is interposed between a lamp and an object (a body to be treated), so that the object is irradiated with light from the lamp through this light transmissive columnar body.
In a heating method using a lamp as a heating source, since the light to be emitted from the lamp is dispersible and the uniformity of the lamp is caused to be reflected in the light, it has been very difficult to perform the heating with excellent uniformity. Further, since the heating source is positioned in the vicinity of the object, it is difficult to effectively cool the object after heating. Additionally, since a reaction atmosphere gives an influence to the external wall of lamp when the heating is performed under a reaction atmosphere, the lamp itself may be badly affected in the heating.
With a view to overcome these problems, the present inventors have developed a method wherein a light transmissive columnar body such as a quartz rod is interposed between a lamp and an object, thereby enlarging the distance between the heating source and the object and at the same time, allowing the light from the lamp to be taken up by the light transmissive columnar body so as to allow the light introduced into the light transmissive columnar body to be reflected several times by the wall surface of the light transmissive columnar body before the light is emitted out of the light transmissive columnar body.
Since light of excellent uniformity is allowed to emit from the light transmissive columnar body in this method, it is possible, through the irradiation of this light onto an object, to perform a uniform heating of the object. Moreover, since the heating source can be placed far away from the object, the maintenance of the apparatus can be facilitated.
However, there are still problems even in this method as explained below. Namely, although the light emitted from the light transmissive columnar body is excellent in uniformity as compared with the light emitted from a lamp, a reduction of optical intensity is caused to occur at the corner portions of the light transmissive columnar body, thereby making it difficult to realize a sufficient uniformity of light depending on the distance between the object and the light irradiating face of the light transmissive columnar body. Further, in the case of heating using a lamp as a heat source, when the input power to the lamp is altered through the changes of voltage, the color temperature of the lamp is also caused to change, thereby changing the radiant heat and hence, making it difficult to suitably control the heating temperature.
As explained above, even with the heating method wherein a light transmissive columnar body is interposed between a heating lamp and an object, it is still difficult to realize a sufficient uniformity of heating depending on the distance between the object and the light irradiating face of the light transmissive columnar body, or to suitably control the heating temperature.
In the meantime, on the occasion of forming a liquid film over a treating substrate in the process of developing a resist film on the surface of treating substrate such as a semiconductor substrate or in the process of performing a wet etching of a treating substrate, a heat transfer is caused to occur between the treating substrate and the liquid film due to the heat of vaporization on the surface of the liquid film, thus giving rise to the phenomenon of lowering the temperature of the treating substrate.
The generation of this phenomenon is more prominent especially at the peripheral region of the treating substrate. Therefore, due to this phenomenon, the treatment of the treating substrate tends to be retarded at the peripheral region thereof, thus deteriorating the uniformity of working.
Further, due to the endothermic or exothermic phenomenon to be generated on the occasion of treatment such as the developing step or wet etching step in a so-called resist process, a temperature distribution is caused to generate on the surface of a treating substrate, thus deteriorating the uniformity of working.
Japanese Patent Examined Publication No. 6-93440 discloses a apparatus wherein a vertical wall of a susceptor (light guide) surrounding a lamp is used as a light reflecting surface, and a light energy reflected by the light reflecting surface is supplied to the object. In this apparatus, however, a heat generated in the light guide is supplied to the object, and thus deteriorating an uniformity of the temperature of the object. Further, since the guide and the lamp are integrally formed, it is necessary to arrange means for dissipate a heat. For that reason, it is necessary to form a space in the guide.
The present invention provides a method in which a heat accumulated in the susceptor (light guide) is not transferred to the object, a second light guide consisting of a light transmissive columnar body is arranged beyond and contiguous with the susceptor (light guide) to unlimitedly decrease a light intensity distribution on the light-irradiating surface of the second light guide and to unlimitedly decrease a heat amount generated in the second light guide. According to the present invention, it is possible to supply a light energy to the object with high uniformity and high efficiency.